Strain gauges for the continuous monitoring of blood pressure, intracranial pressure, or the like in electric isolation from the patient even at the high voltages encountered in defibrillators which might be used on cardiac patients, have been well known for some time. Typically, prior art gauges of this type have had to be enclosed in an extremely rigid, relatively heavy housing of machined thermosetting materials or metals which would undergo no measurable deformation when handled by medical personnel. Because of their sturdy construction, such prior art gauges were expensive and did therefore not lend themselves to use as disposable sensing devices.
Some disposable prior art devices have been made, but these provided the electrical insulation needed between the measured fluid and a diffused silicon chip strain gauge by interposing a plug of silica gel between the fluid and the strain gauge. The silica gel would transmit the pressure of the fluid to the strain gauge but would prevent the formation of a ground path through the patient as long as the silica gel plus was properly in place. This arrangement limited the usefulness of prior art disposable gauges because it was possible for the silica gel to migrate and allow fluid to contact the strain gauge circuitry.